At least three major glycoproteins of human platelet membranes have been defined, purified and characterized. One glycoprotein (GPI) which is absent from the surface of Bernard-Soulier platelets also may be associated with the ristocetin receptor. Our current project proposes to purify sufficient quantities of each of these glycoproteins to allow immunization of rabbits or goats and thereby obtain specific antiserum for each glycoprotein. Preparations of monoclonal antibodies is also possible. These antisera would then be used to evaluate the presence of each glycoprotein on platelets from patients with thrombosis or bleeding problems. In addition, the antisera can be used to probe the receptor function of each glycoprotein and, using the flow cytometer technology, quantitate these glycoproteins on the surface of normal and abnormal platelets. The study will prepare glycoproteins from the platelets of normal human volunteer donors. Our recently acquired high pressure liquid chromatography system will facilitate the analysis and purification of these platelet membrane glycoproteins.